Recent government regulatory policies requiring a reduction of volatile organic emissions (VOC) in coating processes has focused attention on:
Electrostatic atomization application methods can improve the transfer efficiency of coatings processes from 30-40% for conventional air spray to 70-95% for a well managed electrostatic process. The concurrent use of high solids coating compositions can further eliminate up to 60%-90% of the VOC emissions from a conventional coating process.
Conductive coatings are prepared by the incorporation of conductive pigments and/or fillers to a non-conductive binder. The concentration of the conductive pigments or fillers is such that in the final film each conductive pigment or filler particle is in contact or near contact with each of the surrounding conductive pigment particles in the film. The required conductive property of these coatings requires the volume concentration of the conductive pigments or fillers to be near, at or just above the critical pigment volume concentration (CPVC).
The electrostatic application of a paint requires that the liquid material be highly resistive or nearly non-conductive. Since resistivity is the reciprocal of conductivity, it is apparent that the paint must have a stable high resistivity while in the liquid form but after application and film formation have a low resistivity or be conductive. In conventional lower solids (7-20%) conductive coatings compositions, it is possible to formulate liquid compositions which will form conductive dry films, and yet have high resistivities in the liquid form. The extra solvent used in the formulation has two functions:
The current regulatory policy of emission reduction with respect to volatile organic compounds (VOC) has outdated the conventional lower solids technology for the manufacture of these types of conductive coatings. Removal of the extra solvent in the conventional formulation not only causes an unacceptable increase in viscosity but forces the conductive pigments and/or fillers into close proximity within the liquid material, and as a result these liquid coating formulations have been shown to short out the charging circuits of electrostatic application devices. It is theorized that resistive failure in these formulations may be caused by two phenomena:
It may be that both mechanisms of failure are operable, but regardless of the cause of the problem, compositions of the present invention have been shown to solve the confounding requirements of: